Wake up device for a communications system

ABSTRACT

The present invention teaches a communications system comprising a first communications device for receiving data and a wake up signal. The first communications device comprises an active mode of operation and a sleep mode of operation for reducing power consumption. Further, the system comprises means for switching the first communications device to and from sleep mode in response to receiving the wake up signal. Further, the system comprises a second communications device for transmitting data to the first device during its active mode, while transmitting the wake up signal to the first device during its sleep mode.

FIELD OF THE INVENTION

The present invention relates to a communication systems. Moreparticularly, the invention pertains to a multi-mode communicationssystem.

BACKGROUND OF THE INVENTION

Recently, there has been increased research and development with respectto Radio Frequency Identification (“RFID”) device tags. These RFID tagsessentially comprise small radio transceivers attached to a movableobject. By coupling an RFID tag to an object, it has been intent ofdevelopers of creating a system for tracking the whereabouts andidentification of the object.

Several RFID systems have been developed. Generally, these designs havebeen relatively large in size—approximately cigarette package—and havebeen generally fabricated using hybrid circuit techniques. Besides theirbulky size, the systems require the RFID tag to constantly remainactivated.

Recently, there have been several breakthroughs in techniques in thedesign and manufacture of RFID tags. Examples of these include “RadioFrequency Identification Device (RFID) and Method of Manufacture,Including an Electrical Operating System and Method,” U.S. patentapplication Ser. No. 899,777, filed on Jun. 17, 1992, “Anti-Theft Methodfor Detecting The Unauthorized Opening of Containers and Baggage,” U.S.patent application Ser. No. 921,037, Jul. 24, 1992, “ElectricallyPowered Postage Stamp or Mailing or Shipping Label Operative with RadioFrequency (RF) Communications,” U.S. patent application Ser. No.928,899, filed on Aug. 12, 1992, and “Modulated Spread Spectrum in RFIdentification Systems Method,” U.S. patent application Ser. No.032,384, filed on Mar. 17, 1993, all commonly assigned to MicronSemiconductor, Incorporated, and all incorporated herein by reference.

It has been thus a design criteria that these RFID tags be light weightand inexpensive. However, these systems previously have not addressedthe need of low power consumption. Presently, RFID tags must be activeto detect their location, as well as additional information. As such,there is a need to develop a RFID tag communications system having anactive mode for receiving/transmitting data and a sleep mode forreducing power consumption.

SUMMARY OF THE INVENTION

In order to achieve the benefits of the present invention, a system isdisclosed comprising a first communications device for receiving dataand a wake up signal. The first communications device comprises anactive mode of operation and a sleep mode of operation for reducingpower consumption. Further, the system comprises means for switching thefirst communications device to and from sleep mode in response toreceiving the wake up signal. Further, the system comprises a secondcommunications device for transmitting data to the first device duringits active mode, while transmitting the wake up signal to the firstdevice during its sleep mode.

Moreover, a method is disclosed for reducing the consumption of energyin operating a communications system. The communications systemcomprises a transmitter, a master receiver and a wake up receiver. Themaster receiver has at least an active mode and a sleep mode ofoperation and the wake up receiver using substantially less power thanthe master receiver. Initially, data is transmitted to and received bythe master receiver during its active mode, while a wake up signal istransmitted and received by the wake up receiver during the masterreceiver's sleep mode. It should be noted that the wake up signalcomprises a predetermined frequency and a predetermined rate of datatransmission. Subsequently, the predetermined frequency and apredetermined rate of data transmission signal are detected. Upondetecting both, the master receiver is enabled for receiving data systemin response to detecting the wake up signal.

The objects and advantages of the present invention will become apparentto those skilled in the art from the following detailed description readin conjunction with the appended claims and the drawings attachedhereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limitative embodiments, with reference tothe attached drawings, wherein below:

FIG. 1 is an high level architecture of the present invention;

FIG. 2 is a flow chart illustrating the method of the present invention;

FIG. 3 illustrates a first embodiment of the present invention; and

FIG. 4 illustrates a second embodiment of the present invention.

It should be emphasized that the drawings of the instant application arenot to scale but are merely schematic representations and are notintended to portray the specific parameters or the structural details ofthe invention, which can be determined by one of skill in the art byexamination of the information herein.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a wake up device for a communications system isillustrated. As shown, the system comprises a first and secondcommunications devices; a transmitter 10 and a receiver 12. Transmitter10 is coupled to antenna 5 in order to properly transmit data and a wakeup signal to receiver 12. Receiver 12 comprises a wake up receiver 20and a master receiver 25, which are both coupled to antenna 15. Further,receiver 12 comprises a switch, which enables the substantial energysavings. It should be noted that the issue of energy saving with respectto transmitter 10 is not important as it is not coupled to an RFID tag,unlike is receiver 12 in the preferred embodiment.

To accomplish these energy savings, master receiver 25 comprises atleast two modes of operation. In the preferred embodiment, the firstmode is referred to as an active mode of operation and the second modereferred to as a sleep mode. Further, wake up receiver 20 requiressubstantially less power for its operation than master receiver 25.

In the active mode of operations, master receiver 25 functions as atraditional receiver, capable of receiving data transmitted bytransmitter 10. By contrast, in order to reduce power consumption duringperiods of inactivity, master receiver 25 comprises a sleep mode. Duringsleep mode, master receiver 25 utilizes a minimal amount of energy forbiasing purposes. Thus, by utilizing this design scheme, a substantialpower savings from receiver 12 can be achieved, which directlycorresponds to the life expectancy of battery powered receiver 12. Forexample, in one receiver design, a 98% power savings has been observed.

Coupled between master receiver 25 and wake up receiver 20, is switch30. Switch 30 switches master receiver 25 between its mode ofoperation—ie., active to sleep mode, as well as sleep mode to activemode—in response to the arrival of a wake up signal. As such,transmitter 10 transmits a wake up signal to receiver 12, which isultimately received by wake up receiver 20. Upon detecting the wake upsignal, a mode change signal is generated to switch 30. Accordingly,switch 30 changes the mode of operation of master receiver.

In the preferred embodiment of the present invention, switch 30 onlyswitches master receiver 25 from sleep mode to active mode. Here, uponreceiving wake up signal, wake up receiver 20 generates a mode changesignal to switch 30. In response, switch 30 senses the mode of operationof master receiver 25. Thus, switch 30 switches master receiver toactive mode upon sensing master receiver 25 as being in sleep mode.Contrarily, switch 30 is inactive upon sensing master receiver 25 asbeing in an active mode of operation. In this embodiment, masterreceiver 25 further comprises a timing scheme which switches masterreceiver from active mode to sleep mode. This timing scheme is enabledwhen a predetermined period passes in master receiver 25 withoutreceiving any data from transmitter 10. The length of the period isdependent on several design criteria including the system's applicationand environment, as well as the desired probabilities of error. In afurther embodiment of the present invention, switch 30, low powerreceiver 20 and master receiver 25 are all positioned on a radiofrequency identification (“RFID”) tag.

Referring to FIG. 2, a flow chart illustrating the method for reducingthe consumption of energy in operating a communications system of thepresent invention employing the architecture described herein.Initially, a wake up signal is transmitted by transmitter 10, andsubsequently, the wake up signal is detected by wake up receiver 20.Finally, the mode of operation of the master receiver 25 is changed inresponse to the detection of the wake up signal.

In one embodiment of the present invention, the step of detecting thewake up signal, itself, comprises a series of steps. First, apredetermined frequency is detected from the wake up signal. In theevent that that frequency is found, a predetermined data rate isdetected from the wake up signal. If that frequency is not found, masterreceiver 25 is kept asleep. In the event that data rate of transmissionof a certain number of bits per second is found, an output signal isgenerated. If that data rate of transmission is not found, masterreceiver 25 is kept asleep. This step of generating an output signalfurther comprises the step of comparing the output signal with areference voltage. By doing so, switch 30 is enabled upon detecting apredetermined frequency and a predetermined data rate of transmissionand master receiver 25 is woken.

Referring to FIG. 3, a first embodiment of the present invention isdepicted. In order to receive a wake up signal, an antenna 50 is coupledwith a frequency detector, realized by a first bandpass filter 55 havinga bandwidth and a radio frequency (“RF”) output. First bandpass filter55, operating in tandem with antenna 59, detects the frequency of thewake up signal. To avert the detection of noise as a wake up signal, thebandwidth of first bandpass filter 55 is substantially narrow.Nonetheless, in the preferred embodiment, first bandpass filter 55 mustdetect a predetermined frequency and a related harmonic.

While the present invention utilizes a narrow bandpass scheme forfrequency detection, it should be obvious to one of ordinary skill inthe art that the frequency detector can be realized using alternatehardware. For example, in place of a narrow bandpass filter, ageneralized filter having an output coupled directly with a comparatorwould achieve the identical functional purpose were the comparator alsofed a frequency reference or source. Another example would be aresonator circuit.

Coupled to bandpass filter 55 is an envelope detector 60. Upon receivingthe RF bandpass output from filter 55, envelope detector 60 demodulatesthe RF bandpass output into a first Base Band (“BB”) signal. Envelopedetector 60 achieves this objective in two steps. However, it should beobvious to one of ordinary skill in the art that the functionalobjective of envelope detector 60 can be realized by alternate means.Initially, envelope detector 60 rectifies the RF bandpass output bymeans of a rectifier. Subsequently, a low pass filter is employed forfiltering the rectified RF bandpass output and forming the first BBsignal.

Once the frequency of the wake up signal has been detected, the presentinvention employs a data rate detector for detecting the rate of datatransmission of the incoming signal, which thereby rejects out of datarate signals. As such, this design employs two means for assessing twocharacteristics of the incoming signal. Thus, by this approach, noiseand/or other sources will not falsely trigger the master receiver intowaking up.

The data rate detector can be realized by a second bandpass filter 70having a second bandwidth and a second BB signal as its output. To avertthe detection of noise as a wake up signal, the second bandwidth ofbandpass filter 55 is substantially narrow bandwidth. In one embodimentof the present invention, the second bandwidth is substantially narrowerthan the first bandwidth of the first bandpass filter. However, in thepreferred embodiment, the second bandwidth need only detect a singularfrequency without any harmonics.

While the present invention utilizes the herein described means for datarate detection, it should be obvious to one of ordinary skill in the artthat the data rate detector can be realized using alternate hardware.For example, a comparator scheme or resonator circuit could be employed.Further, digital circuitry could also be used to accomplish the samepurpose as the data detector described herein.

Further, coupled with second bandpass filter 70 is a second envelopedetector 75. In order to detect the data rate of incoming signal andascertain whether it is the wake up signal, second envelope detector 75generates an output signal corresponding to BB signal input receivedfrom second bandpass filter 70 by demodulating the BB signal input.Second envelope detector 75 achieves this objective in two steps.However, it should be obvious to one of ordinary skill in the art thatthe functional objective of second envelope detector 75 can be realizedby alternate means. Initially, envelope detector 75 rectifies the BBinput signal second bandpass filter 70 by means of a rectifier.Subsequently, a low pass filter is employed for filtering the rectifiedBB signal input. As a result of this architecture, second envelopedetector 75 generates a upward ramped step or a downward ramped stepoutput signal.

Coupled to second envelope detector 75 is a comparator 80. Comparator 80is employed to compare the output signal of second envelope detector 75with a voltage reference. By this arrangement, comparator 80 triggers ainternal wake up₁ signal. Wake up₁ signal is subsequently fed intocontrol logic 85, which is coupled with a data processor 90, for wakingup the master receiver 25.

In an alternate embodiment of the present invention, a second data ratedetector is utilized. Second data rate detector, being coupled to thefrequency detector, receives the first BB signal generated by the firstenvelope detector 60. The second data rate detector can be designed inan identical fashion as the first data detector described herein.

By this arrangement, comparator 80 triggers a internal wake up₂ signalwhich is input into control logic 85, which is coupled with a dataprocessor 90, for waking up the master receiver 25. By employing twodata rate detectors, the wake up receiver can switch the data rate to bedetected from the wake up signal. Here, switching logic 85 incombination with data processor 90 recognize the data rate to bedetected from the wake up signal. Subsequently, when a change isnecessary, a second data rate is selected as being the data rate to bedetected from the wake up signal for the purposes of waking masterreceiver 25.

Moreover, this two data rate detector scheme can also be employed forthe purpose of enabling the wake up receiver to switch modes ofoperation—ie., sleep mode and active mode—as described hereinabove.Thus, when a first data rate is received, master receiver 25 is to bewoken in to active mode, while master receiver 25 is to be put intosleep mode when a second data rate is received.

In a further alternate embodiment of the present invention, a mixer 65is employed. Mixer 65 is coupled between first envelope detector 60 andsecond bandpass filter 70. Mixer 65 is used to provide a means forfrequency translating the RF bandpass output. The extent of thetranslation performed by mixer 65 corresponds to the local oscillator.The local oscillator, having a clock rate of ƒ₁, provides a referenceoscillating signal to the mixer 65.

Referring to FIG. 4, an alternate embodiment of the present invention isillustrated. The architecture disclosed here is further development ofan alternate embodiment of FIG. 3. Here, three data rate detectors areemployed. Third data rate detector, being coupled to the frequencydetector, receives the first BB signal generated by a first envelopedetector 110. The third data rate detector can be designed in anidentical fashion as the first and second data detectors describedherein.

By this arrangement, comparator 130 triggers a internal wake up_(x)signal which is input into control logic 135, which is coupled with adata processor 140, for waking up the master receiver 25. By employingthree data rate detectors, the wake up receiver can switch the data rateto be detected from the wake up signal. Here, switching logic 135 incombination with data processor 140 recognize the data rate to bedetected from the wake up signal. Subsequently, when a change isnecessary, a third data rate is selected as being the data rate to bedetected from the wake up signal for the purposes of waking masterreceiver 25.

In still another embodiment of the present invention, a modulationdetector (not shown) is further incorporate for detecting a modulationscheme. In this embodiment, the wake up signal must also comprise amodulation format or formats. As such, the modulation detector candetect a modulation scheme selected from the group including at leastamplitude modulation, frequency modulation, amplitude shift keymodulation, phase shift key modulation, frequency shift key modulation,and multiphase frequency shift key modulation. The modulation detectorcan be realized by a variety of designs known to one of ordinary skillin the art. Thus, upon receiving the wake up signal, the modulationdetector detects the format of the wake up signal and respondsaccordingly.

While the particular invention has been described with reference toillustrative embodiments, this description is not meant to be construedin a limiting sense. It is understood that although the presentinvention has been described in a preferred embodiment, variousmodifications of the illustrative embodiments, as well as additionalembodiments of the invention, will be apparent to persons skilled in theart upon reference to this description without departing from the spiritof the invention, as recited in the claims appended hereto. For example,it should be obvious to one of ordinary skill in the art that either orboth first and second communications devices, such as transmitter 10 anda receiver 25, can further comprise transceiver properties for thepurposes of the present invention. It is therefore contemplated that theappended claims will cover any such modifications or embodiments as fallwithin the true scope of the invention.

All of the U.S. patents cited herein are hereby incorporated byreference as if set forth in their entirety.

1-26. (canceled).
 27. A radio communications system comprising: a masterreceiver circuit having a sleep mode and an active mode, the masterreceiver circuit being configured to consume less power in the sleepmode than in the active mode; a switch circuit configured to controlwhen the master receiver circuit switches between the sleep mode and theactive mode; a receiver input configured to receive radio signals; and awake-up detector circuit, coupled to the receiver input, including:circuitry configured to reject any of said radio signals not having adata rate equal to a single, specific, predetermined, first data rate,and to generate a wake-up mode signal when the receiver input receives aradio signal having a data rate equal to said first data rate; whereinthe switch circuit switches the master receiver from the sleep mode tothe active mode in response to the data rate detector circuit generatingsaid wake-up mode signal; and wherein the switch circuit does not switchthe master receiver from the sleep mode to the active mode in responseto the receiver input receiving a radio signal having a data rate notequal to said first data rate.
 28. A radio communications systemaccording to claim 27, wherein, while the master receiver circuit is inthe sleep mode, the switch circuit continuously and uninterruptiblymaintains the master receiver circuit in the sleep mode until the datarate detector circuit generates said wake-up mode signal.
 29. A radiocommunications system according to claim 27, further comprising a seconddata rate detector circuit that detects when the receiver input receivesa radio signal having a second data rate, said second data rate beingdifferent from said first data rate, wherein the second data ratedetector is connected to control the switch circuit so as to switch themaster receiver circuit to the sleep mode in response to the receiverinput receiving a radio signal having said second data rate.
 30. A radiocommunications system according to claim 27, and further comprising aradio transmitter, wherein, at a time when the master receiver circuitis in its sleep mode, the radio transmitter transmits a signal havingthe first data rate so as to put the master receiver circuit into itsactive mode, and wherein, at a time when the master receiver circuit isin its active mode, the radio transmitter transmits data to the radiocommunications receiver.
 31. A method of changing a radio communicationsreceiver from a sleep mode to an active mode, comprising: providing aradio communications receiver having a sleep mode and an active mode,wherein the receiver continuously and uninterruptibly consumes lesselectrical power in the sleep mode than in the active mode; receivingradio signals at an input of the receiver; filtering said radio signalsreceived in the receiving step so as to reject any of said radio signalsnot having a data rate equal to a single, specific, predetermined, firstdata rate; while the receiver is in the sleep mode, detecting when thereceiver receives a radio signal that has a data rate equal to saidfirst data rate and that is not rejected by the filtering step; andswitching the receiver from the sleep mode to the active mode inresponse to detecting said first data rate.
 32. A method according toclaim 31, further comprising, while the receiver is in the sleep mode,continuously and uninterruptibly maintaining the receiver in the sleepmode until the receiver receives a radio signal that has a data rateequal to said first data rate and that is not rejected by the filtering.33. A method according to claim 31, further comprising detecting whenthe receiver receives a radio signal having a data rate equal to asecond predetermined data rate, wherein the second data rate isdifferent from the first data rate; and in response to detecting saidsecond data rate, switching the receiver to the sleep mode, and thencontinuously and uninterruptibly maintaining the receiver in the sleepmode until detecting said first data rate again.
 34. A method accordingto claim 31, further comprising: at a time when the receiver is in itssleep mode, transmitting from a radio transmitter a signal having thepredetermined data rate so as to put the master receiver circuit intoits active mode; and at a time when the receiver is in its active mode,transmitting data from the radio transmitter to the receiver
 35. A radiocommunications system comprising: a receiver having a sleep mode and anactive mode such that, in operation, the receiver continuously anduninterruptibly consumes less power in the sleep mode than in the activemode; a receiver input for receiving radio signals; and a wake-updetector circuit coupled to the receiver input including: circuitry thatrejects any of said radio signals not having data rate equal to apredetermined, first data rate, and that generates a wake-up mode signalonly when the receiver input receives a radio signal having a data rateequal to said first data rate; wherein the receiver is configured toswitch from the sleep mode to the active mode in response to the datarate detector circuit generating said wake-up mode signal.
 36. A radiocommunications system according to claim 35, wherein the switch circuitdoes not switch the master receiver from the sleep mode to the activemode in response to the receiver input receiving a radio signal having adata rate not equal to said first data rate.
 37. A radio communicationssystem according to claim 35 further comprising: a second data ratedetector circuit that detects when the receiver input receives a radiosignal having a second data rate, said second data rate being differentfrom said first data rate; wherein the receiver is configured to switchto the sleep mode in response to the receiver input receiving a radiosignal having said second data rate.
 38. A radio communications systemaccording to claim 35 further comprising: a radio transmitter; whereinthe radio transmitter is configured to transmit, at a time when themaster receiver circuit is in its sleep mode, a signal having the firstdata rate so as to put the receiver into its active mode; and wherein,at a time when the receiver is in its active mode, the radio transmittertransmits data to the receiver.
 39. A method of changing a radiocommunications receiver from a sleep mode to an active mode, comprising:providing a receiver having a sleep mode and an active mode, wherein, inoperation, the receiver continuously consumes less electrical power inthe sleep mode than in the active mode; receiving radio signals at aninput of the receiver; rejecting any of said radio signals not having adata rate equal to a predetermined first data rate; while the receiveris in the sleep mode, continuously maintaining the receiver in the sleepmode until the receiver receives a radio signal that has a data rateequal to said first data rate and that is not rejected; while thereceiver is in the sleep mode, detecting when the receiver receives aradio signal that has a data rate equal to said first data rate and thatis not rejected; and switching the receiver from the sleep mode to theactive mode in response to detecting said first data rate.
 40. A methodaccording to claim 39, further comprising the subsequent steps of:detecting when the receiver receives a radio signal having a data rateequal to a second predetermined data rate, wherein the second data rateis different from the first data rate; and in response to detecting saidsecond data rate, switching the receiver to the sleep mode, and thencontinuously maintaining the receiver in the sleep mode until detectingsaid first data rate again.
 41. A method according to claim 39, furthercomprising the steps of: at a time when the receiver is in its sleepmode, transmitting from a radio transmitter a signal having thepredetermined data rate so as to put the master receiver circuit intoits active mode; and at a time when the receiver is in its active mode,transmitting data from the radio transmitter to the receiver.